Genetic and ultrastructural investigations of behavioral mutants of Paramecium are in progress. Genetic studies focus on obtaining and characterizing new types of mutants (receptor potential mutants, temperature-sensitive paranoiacs, X-ray-induced paranoiacs, Ca-gate mutants) and suppressors of known mutants. A suppressor of pawn B behaves genetically in an anaomalous fashion perhaps consistent with a transposable element. A new dominant paranoiac has been mapped at or near the fna locus which has both a fast and a recessive paranoiac allele previously described. Ultrastructural studies reveal abnormalities in the morphology of plaques of membrane particles at the base of cilia in some paranoiac stocks suggesting an involvement of these particles in Na ion/K ion transport. Two paranoiac stocks, fna fast-1, and a tetraethylammonium-insensitive stock, have less well-organized and/or smaller plaques than wild-type; two other paranoiac stocks are not distinguishable from wild-type; one paranoiac has slightly larger and more regular plaques than wild-type. Different paranoiacs have somewhat different behavioral phenotypes also. Cilia can be removed from paramecia without killing the cells. Observations of behavior during regeneration of cilia are in progress.